Synthetic membranes have changed today’s world in areas such as (i) water desalination and disinfection, (ii) medical treatment for open heart surgery and kidney support, (iii) chemical, gas and bioprocess engineering. These disruptive developments have only been able to emerge when multiple disciplines such as materials science, fluid mechanics, device design and process system developement were integrated. Unfortunately, today’s scientific membrane community focuses predominantly on the development of new materials aiming for superior transport properties inside the membrane: too little attention is paid to the molecular transport resistances outside the membrane material at the membrane-fluid interface. The potential of new membrane materials will remain ineffective as high and selective transport rates always go along with molecular transport resistances emerging at the membrane-fluid interface in the form of diffusion limitations in the laminar boundary layers. In order to make full use of the very many new materials, also new means to control and minimize such fluid based resistances need to be developed.
With respect to the prevailing challenge of fluid related resistances in membrane separation processes, the proposed research develops a rigorous methodology to control and improve mass transport through the membrane-fluid interface. Therefore “Controlling Fluid Resistances at Membranes” (ConFluReM) establishes strategic tools in fabrication, characterization, and simulation to develop new instruments to:
i) comprehend and quantify the prevalent mass transport resistances in representative membrane separation processes,
ii) synthesize and fabricate nano-, micro- and mesoscale material systems as instruments to control and overcome the limitations of concentration polarization and fouling,
iii) ultimately control and overcome the negative influence of concentration polarization and concentration polarization induced fouling and scaling.
During the project, mass transport resistances were visualized by analyzing fluid and particle movement around the membrane surface. In many cases, these resistances could be efficiently reduced by introducing targeted mixing around the membrane-fluid interface. For example, for electrically driven water desalination, printed polymer patterns on top of the membrane were shown to induce vortices that mix the laminar boundary layer and reduce its resistance. For filtration and oxygenation applications, hollow fiber membranes with built-in static mixers were produced. These mixers induce additional turbulence close to the membrane, counteract membrane fouling and enhance mass transport. Many of these advances have been tested on the process scale and enabled more efficient and sustainable water desalination, energy storage in redox flow batteries, or blood oxygenation.
